| Message ID | 1471960185-14044-1-git-send-email-ming.lei@canonical.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Tue, Aug 23, 2016 at 09:49:45PM +0800, Ming Lei wrote: > After arbitrary bio size is supported, the incoming bio may > be very big. We have to split the bio into small bios so that > each holds at most BIO_MAX_PAGES bvecs for safety reason, such > as bio_clone(). > > This patch fixes the following kernel crash: > > > [ 172.660142] BUG: unable to handle kernel NULL pointer dereference at 0000000000000028 > > [ 172.660229] IP: [<ffffffff811e53b4>] bio_trim+0xf/0x2a > > [ 172.660289] PGD 7faf3e067 PUD 7f9279067 PMD 0 > > [ 172.660399] Oops: 0000 [#1] SMP > > [...] > > [ 172.664780] Call Trace: > > [ 172.664813] [<ffffffffa007f3be>] ? raid1_make_request+0x2e8/0xad7 [raid1] > > [ 172.664846] [<ffffffff811f07da>] ? blk_queue_split+0x377/0x3d4 > > [ 172.664880] [<ffffffffa005fb5f>] ? md_make_request+0xf6/0x1e9 [md_mod] > > [ 172.664912] [<ffffffff811eb860>] ? generic_make_request+0xb5/0x155 > > [ 172.664947] [<ffffffffa0445c89>] ? prio_io+0x85/0x95 [bcache] > > [ 172.664981] [<ffffffffa0448252>] ? register_cache_set+0x355/0x8d0 [bcache] > > [ 172.665016] [<ffffffffa04497d3>] ? register_bcache+0x1006/0x1174 [bcache] Acked-by: Kent Overstreet <kent.overstreet@gmail.com> -- To unsubscribe from this list: send the line "unsubscribe linux-block" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 08/23/2016 07:49 AM, Ming Lei wrote: > After arbitrary bio size is supported, the incoming bio may > be very big. We have to split the bio into small bios so that > each holds at most BIO_MAX_PAGES bvecs for safety reason, such > as bio_clone(). > > This patch fixes the following kernel crash: > >> [ 172.660142] BUG: unable to handle kernel NULL pointer dereference at 0000000000000028 >> [ 172.660229] IP: [<ffffffff811e53b4>] bio_trim+0xf/0x2a >> [ 172.660289] PGD 7faf3e067 PUD 7f9279067 PMD 0 >> [ 172.660399] Oops: 0000 [#1] SMP >> [...] >> [ 172.664780] Call Trace: >> [ 172.664813] [<ffffffffa007f3be>] ? raid1_make_request+0x2e8/0xad7 [raid1] >> [ 172.664846] [<ffffffff811f07da>] ? blk_queue_split+0x377/0x3d4 >> [ 172.664880] [<ffffffffa005fb5f>] ? md_make_request+0xf6/0x1e9 [md_mod] >> [ 172.664912] [<ffffffff811eb860>] ? generic_make_request+0xb5/0x155 >> [ 172.664947] [<ffffffffa0445c89>] ? prio_io+0x85/0x95 [bcache] >> [ 172.664981] [<ffffffffa0448252>] ? register_cache_set+0x355/0x8d0 [bcache] >> [ 172.665016] [<ffffffffa04497d3>] ? register_bcache+0x1006/0x1174 [bcache] > > The issue can be reproduced by the following steps: > - create one raid1 over two virtio-blk > - build bcache device over the above raid1 and another cache device > and bucket size is set as 2Mbytes > - set cache mode as writeback > - run random write over ext4 on the bcache device Applied for 4.8, thanks.
diff --git a/block/blk-merge.c b/block/blk-merge.c index 3eec75a..f6ae884 100644 --- a/block/blk-merge.c +++ b/block/blk-merge.c @@ -94,9 +94,31 @@ static struct bio *blk_bio_segment_split(struct request_queue *q, bool do_split = true; struct bio *new = NULL; const unsigned max_sectors = get_max_io_size(q, bio); + unsigned bvecs = 0; bio_for_each_segment(bv, bio, iter) { /* + * With arbitrary bio size, the incoming bio may be very + * big. We have to split the bio into small bios so that + * each holds at most BIO_MAX_PAGES bvecs because + * bio_clone() can fail to allocate big bvecs. + * + * It should have been better to apply the limit per + * request queue in which bio_clone() is involved, + * instead of globally. The biggest blocker is the + * bio_clone() in bio bounce. + * + * If bio is splitted by this reason, we should have + * allowed to continue bios merging, but don't do + * that now for making the change simple. + * + * TODO: deal with bio bounce's bio_clone() gracefully + * and convert the global limit into per-queue limit. + */ + if (bvecs++ >= BIO_MAX_PAGES) + goto split; + + /* * If the queue doesn't support SG gaps and adding this * offset would create a gap, disallow it. */